1. Field of the Invention
The present invention relates to an improvement in an internal speed-reduction type starter equipped with an epicyclic reduction gear.
2. Discussion of the Background
FIG. 1 shows as an example a conventional internal speed-recution type starter 1. In FIG. 1, a reference numeral 2 designates a d.c. motor, a numeral 3 designates a front bracket supporting the d.c. motor by means of long bolts (not shown in drawing), a numeral 4 designates an electromechanical switching means, typically a solenoid, attached to the front bracket and a numeral 5 designates the yoke of the d.c. motor 2 onto the inner surface of which magnetic field poles 6 formed of ferrite permanent magnet are fixed. In the inner circumferential surface of the front end portion of the yoke 5, a circular seat portion 5a is formed and a ring gear 8 as a structural element of an epicyclic reduction gear 7 is fitted to the circular seat portion 5a. The ring gear 8 is firmly attached with a flange 9 which is supported through a sleeve bearing 11 by a pinion shaft 10 as an output rotary shaft of the epicyclic reduction gear 7. A flange 12 is firmly attached to or formed integrally with an end portion of the pinion shaft 10. A supporting pin 14 is set up on the side surface of the flange 12 to have a function as an arm for pivotally supporting a planet gear 13 through a sleeve bearing 15.
An armature 16 is secured on an armature rotary shaft 17 which is provided with a spur gear 18 at its front end portion with which the planet gear 13 is always interlocked to be driven. A reference numeral 19 designates an armature iron core and a numeral 20 designates an armature winding. A sleeve bearing 21 is fitted to an annular space formed between the outer peripheral surface at the front end of the armature rotary shaft 17 and inner peripheral surface of a recess 10a formed in the rear end of the pinion shaft 10 so as to support the front end of the shaft 17 in a freely rotatable manner. A steel ball 22 is provided between the rear end of the pinion shaft 10 and the front end of the armature rotary shaft 17 to bear thrust of the both shafts. An overrunning clutch 23 comprises a clutch outer member 24 which is connected to the pinion shaft 10 so as to be slidable in the axial direction of the pinion shaft 10 through a helical spline 25 formed in the outer surface of the pinion shaft 10. A frictional roller 26 is placed in a wedge-like space formed between the clutch inner member 27 and a cam surface 24a formed on the inner circumferential surface of the clutch outer member 24, the frictional roller 26 being engaged with the narrow area of the wedge-like space. A washer 28 is secured to the clutch outer member 24 by caulking of a cover 29 to assemble structural elements of the overrunning clutch 23 as shown in FIG. 1. A pinion 30 is fixed to the front end of the clutch inner member 27. A sleeve bearing 31 is fitted between the pinion shaft 10 and the inner peripheral surface of the pinion 30 so that the pinion 30 is slidable on and along the pinion shaft 10 in its axial direction. A stopper 32 is secured to the pinion shaft 10 by means of a ring 33 to act as a detent for preventing the overrunning clutch 23 from its forward projection. A sleeve bearing 34 is fitted to a projecting part 3a of the front bracket 3 to support the front end of the pinion shaft 10 in a freely rotatable manner. There is placed a shift lever 35 having one end connected to the clutch outer member 24 of the overrunning clutch 23 through a cam-engagement and the other end (the upper end) connected to a plunger 36 of solenoid 4 through a cam-engagement. The shift lever 35 is turned around a turnable fulcrum point 35a by actuating the plunger 36. A holder 37 supporting the turnable fulcrum point 35a of the shift lever 35 is loosely fitted in a recess 3b of the front bracket 3 so as to be movable in the axial direction. A force applied to the holder 37 to support the shift lever 35 is received by the front bracket 3. A lever spring 38 is placed in the recess 3b to urge the holder 37 towards the inner surface of the front bracket 3a. A grommet 39 is placed to receive a repulsive force of the lever spring 38.
Operations of the conventional starter having the construction as above-mentioned will be described.
Actuation of the electromagnetic switch 4 causes operations of structural elements of the starter as follows: the plunger 36 is attracted into a casing (in the left direction in drawing); the shift lever 35 is turned around the turnable fulcrum point 35a in the counterclockwise direction; the overrunning clutch 23 is moved fowardly (in the right direction) along the pinion shaft 10; the front end of the pinion 30 comes in contact with the stopper 32 and the pinion 30 is brought to interlocked with a ring gear (not shown) of an internal combustion engine although it is not shown in the drawing.
While the operations as above-mentioned are effected, the main contact (not shown) of the solenoid switch 4 is closed by the actuation of the plunger 36. Then, the armature 16 is connected to a d.c. power source (which may be a battery) through the main contact whereby there takes place a torque in the armature rotary shaft 17 due to excitation of magnetic poles 6. When the rotational force is applied to a planet gear 13 through the spur gear 18 formed on the armature rotary shaft 17, the planet gear 13 rolls around the rotary shaft 17 while interlocking with teeth formed inside the ring gear 8 to thereby increase a torque by speed-reducing function of the epicyclic reduction gear 7. The rotational force is transmitted to the pinion shaft 10 so that the ring gear for effecting initiation of the internal combustion engine is driven by the pinion shaft 10 through the helical spline 25, the clutch outer member 24, the cam surface 24a, the frictional roller 26, the clutch inner member 27 and the pinion 30. After the internal combustion engine is started, the pinion 30 is driven at an excessive speed by the ring gear. A rotational force caused by the excessive revolution, namely reversely driving force makes a relative rotation between the cam surface 24a and the clutch inner member 27 to be opposite whereby the frictional roller 26 disconnects the clutch inner member 27 from the clutch outer member 24. Then, only the pinion 30 rotates along with the ring gear for effecting initiation of the engine to release the rotational force caused by the excessive revolution applied to the structural elements preceeding the overrunning clutch 23. When the solenoid 4 is deenergized, the plunger 36 is moved in the right direction by the action of a coil spring held in the casing and it returns at a position as shown in FIG. 1, with the result that the overrunning clutch 23 is retracted to disconnect the pinion 30 from the ring gear (not shown).
Thus, in the conventional device, the two rotary shafts 10, 17 are separately disposed in the axial direction and supporting structure for each of the rotary shafts is complicated and accordingly, it is disadvantageous that the circular seat portion 5a is apt to be bent and it is difficult to for the structural elements to have mechanical strength in view of restriction in structure.